Solid state light sources such as light emitting diodes (LEDs) generate visible or non-visible light in a specific region of the electromagnetic spectrum. An LED may output light, for example, in the blue, red, green or non-visible ultra-violet (UV) or near-UV region(s) of the electromagnetic spectrum, depending on the material composition of the LED. When it is desired to construct an LED light source that produces a color different from the output color of the LED, it is known to convert the LED light output having a peak wavelength (“primary light”) to light having a different peak wavelength (“secondary light”) using photoluminescence.
Photoluminescence generally involves absorbing higher energy primary light by a wavelength converting material (“conversion material”) such as a phosphor or mixture of phosphors. This absorption excites the conversion material to a higher energy state. When the conversion material returns to a lower energy state, it emits secondary light, generally of a longer wavelength than the primary light. The peak wavelength of the secondary light can depend on the type of phosphor material. This process may be generally referred to as “wavelength conversion.” An LED combined with a wavelength converting structure that includes a conversion material such as phosphor to produce secondary light may be described as a “phosphor-converted LED” or “wavelength converted LED.”
In a known configuration, an LED die such as a III-nitride die is positioned in a reflector cup package and a volume. To convert primary light to secondary light, a wavelength converting structure may be provided. The wavelength converting structure may take the form of a self supporting “plate,” such as a ceramic plate or a single crystal plate. In any case, the plate may be attached directly to the LED, e.g. by wafer bonding, sintering, gluing, etc. Such a configuration may be understood as “chip level conversion” or “CLC.” Alternatively, the plate may be positioned remotely from the LED. Such a configuration may be understood as “remote conversion.”
Recently, interest has grown in wavelength converting structures that included one or more thin films of wavelength conversion material. While such thin film converters can be effective for converting primary light to secondary light, it can be challenging to incorporate them into existing processes for manufacturing LEDs. For example, thin film converters require the use of a substrate to support the thin film of conversion material. In many instances, few substrate options are available that can withstand high temperature processing of the conversion material. While sapphire substrates can be used, processing such substrates into a conformation that is compatible with an LED die is a challenge, particularly if the LED die includes a bond pad that requires the use of a converter including one or more curved notches. Moreover, precise placement of the conversion plate and orientation of the conversion layers relative to the LED die is often important. While such positioning can be achieved using high speed “pick and place” production, significant hard tooling and in some instances human interaction is needed to ensure that a thin film converter is properly positioned and oriented. This can increase the expense and complexity of the LED manufacturing process.